Award Date

December 2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry and Biochemistry

First Committee Member

David W. Hatchett

Second Committee Member

Spencer Steinberg

Third Committee Member

Bryan Spangelo

Fourth Committee Member

Terry Spell

Number of Pages

90

Abstract

The purpose of this research is to show that the electrochemically controlled formation of monometallic and bimetallic catalysts in polyaniline (PANI) can directly influence the efficiency and reproducibility of the catalytic oxidation of methanol. PANI is a conductive polymer that provides a three-dimensional template for the metallic catalysts deposition at nitrogen sites. The controlled deposition of metallic species can be achieved using the normal oxidation/reduction cycles of PANI. The deposition of metallic species relies on anion precursors that are electrostatically bound by the polymer during the oxidation cycle. The precursor is reduced directly at the nitrogen sites in the polymer on the reverse cycle. While noble metal precursors such as AuCl4 - , PdCl4 2- and PtCl4 2- are available commercially, less expensive transition metal precursors were prepared in our lab. For example, the precursor NiCl4 2- was prepared by

reacting dimethylamine hydrochloride with NiCl2 in the presence of chloroform based on the following chemical reaction:

2[(CH3)2NH2Cl] + NiCl2 → [(CH3 )2NH2 ]2 ∙NiCl4

For proof of principal, solutions containing [(CH3)2NH2]2·NiCl4 were utilized to achieve Ni deposits at graphitic electrodes prior to deposition in PANI. PANI/metallic catalysts containing single metal species including Au, Pd, and Pt are well known and have been the

subject of many studies in our laboratory. However, it is clear from the previous results that significant poisoning of the catalyst occurs during the oxidation of methanol. 1-6 The byproducts of the oxidation reaction adsorb onto the metal surface poisoning or blocking further catalysis. However, PANI/bimetallic composite can be prepared providing better catalytic oxidation of alcohol with reduced poisoning of the metal catalyst surface. Bimetallic catalysts are achieved when nickel is electrochemically deposited onto gold in the polymer. The combination of two different metal species reduces the deposition of surface contaminants ensuring oxidation of

methanol can occur at the catalyst surface. The bimetallic catalyst containing Ni rather than two noble metal species also reduces the cost associated with the oxidation of methanol. The controlled deposition of the bimetallic catalyst in PANI showed high reproducibility in solutions containing KOH and during methanol oxidation. The SEM/EDX analysis confirms the deposition of Au/Ni in PANI. Finally, PANI/Au/Ni composites show that surface poisoning is minimized in comparison to PANI/Au composites. However, PANI/Ni composites showed higher current density for methanol oxidation at Ni in comparison to PANI/Au/Ni composites.

Keywords

Bisdimethylammonium tetrachloronickelate; Direct Methanol Fuel Cells; Methanol Oxidation; Ni chloride metal complex; PANI/Ni Composite; Polyaniline

Disciplines

Chemistry | Inorganic Chemistry | Polymer Chemistry

Language

English


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